The long-term goal of this project is to elucidate the signaling mechanisms underlying activity-dependent synapse formation. We have demonstrated that the secreted glycoprotein Wingless (Wg/Wnt-1), best known for its crucial role in early morphogenesis and pattern formation, is also a fundamental organizer of glutamatergic synapses in the fruit fly Drosophila. Our current studies implicate Wnts in rapid, activity-dependent, structural and functional synaptic modifications. In humans, misregulation of Wnt signaling is associated with a number of cognitive disorders, such as schizophrenia, bipolar disorder, and Alzheimer's disease. Therefore, understanding the mechanisms of Wnt signaling in the nervous system will have important implications for our ability to design clinical strategies to treat these diseases. In this project our experimental approach makes extensive use of live imaging, including that of completely intact animals, combined with electron microscopy, molecular genetics, and electrophysiology to investigate the mechanisms by which activity induces the secretion of Wg and promotes new synaptic formation. We will also explore the synaptic role of Evenless Interrupted/ Wntless/Sprint, a multipass transmembrane protein recently discovered to be critical in epithelial Wg secretion. In particular we will (1) determine the role of electrical activity in Wg synthesis, trafficking and release, (2) determine the significance and molecular mechanisms of activity and Wg-dependent synaptic plasticity, and (3) determine the role of Evi at synapses and test the hypothesis that at the NMJ Evi mediates novel trans-synaptic signaling. We expect our findings will bring about important insights into the general nature of synapse plasticity, as these fly synapses show a considerable degree of molecular conservation with mammalian central synapses, and as Wnts are also involved in mammalian systems during synapse differentiation and long-term modifications in synaptic function.